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Nature Nut: Sponges in Mexico have distant cousins near Mayowood

January 6, 2019

Shortly after arrival in Cozumel with my daughters’ families, I jumped into the water to look at the wall.

The wall, an underwater feature near the island, is full of hundreds of fish, along with many varieties of coral. It runs a quarter mile in both directions from the Cozumel Island condo where Linda and I, and other family members and friends, spent many winter weeks over the past 13 years. Ten to 15 feet tall, it harbors other organisms besides the fish and coral, but one of the simplest is also quite dominant on the wall.

Sponges of many shapes, colors and sizes can be seen on the wall, as well as the bottom near the wall. When I go out on a dive boat a quarter- to half-mile off shore, the reefs there harbor sponges so large I could probably crawl into some of them. Based on growth rates, some of the larger barrel sponges are estimated to be thousands of years old.

I recall from a high school biology class that sponges are simple animals, often mistaken for plants because they do not move from place to place. They don’t have organs, so no nervous, digestive, or circulatory systems. But, they do circulate a constant flow of water through their body to withdraw food and oxygen and to get rid of waste.

As one of the groups branching off the evolutionary trunk of all animals, they are considered a “sister group” ancestor of all other animals, including humans. Most all sponges are marine, found in oceans throughout the world at depths ranging from inches to more than five miles. However, there are a few freshwater sponges, some of which I remember finding below the Mayowood Dam with high school biology classes I took there for studies in what seems like another lifetime.

Most of the thousands of known sponge species feed on bacteria and other minute food particles, although some host photosynthesizing organisms that provide food for the sponge. In some cases, sponges are known to consume miniscule crustaceans. Some sponges, in turn, are consumed by turtles and fish.

I can’t remember ever seeing two sponges that look exactly alike. Most are asymmetrical, meaning they don’t have mirror image halves like many animals, including humans. They come in a myriad of colors and shapes and I have even seen one kind of sponge growing on another.

Sponges are supported by internal skeletons made up of a rubbery spongin, or little spear-like spicules, or both. I recall taking a small sample of the freshwater sponges we found at Mayowood back to the classroom. Looking at them under a microscope, the glassy spicules were quite easy to see.

Sponges provide habitat for many other forms of marine life, with some large varieties housing thousand of “guests.” They are also valuable to researchers for the chemicals they produce that may fight cancer.

While most sponges I’ve touched are relatively soft feeling, some have a hard surface. Many that have entirely soft fibrous skeletons have been used by humans over thousands of years as padding or cleaning tools. However, due to overharvesting, this industry came close to total collapse, and most sponges now bought by humans are synthetic.

In the U.S., a sponge industry still exists in Florida, although at a fraction of what it once was. Five species are currently harvested, with three for functional purposes and two mostly for decoration. Take quotas are carefully set and monitored and, in some ways, the harvesting is sustainable, as leaving a small piece of sponge will allow it to grow back.

Sponges need to be cleaned and dried when harvested, removing the outer skin, shaking out much of the internal tissue, and eventually having only the sponge skeleton left. Since I don’t recall using real sponges, I’ll look forward to hearing back from any readers who have.

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